SIMS analysis of oxynitrides: evidence for nitrogen diffusion induced by oxygen flooding

Dual-beam time-of-flight secondary ion mass spectrometry (ToF-SIMS) and low -energy SIMS can easily give a qualitative nitrogen depth profile through o xynitride structures. However, the use of different measurement conditions (polarity, primary ions, etc) shows that interpretation of the results is n ot straightforward and can lead to different artefacts, particularly with r espect to the nitrogen peak position and (apparent) tailing of the nitrogen into the underlying silicon, Because concurrent ionization yield changes i nfluence the profile interpretation, oxygen flooding in combination with Ar + sputtering has been used in this paper to separate ion beam mixing and io nization yield effects. The results indicate that the distortions of the nitrogen profiles originat e from two combined effects. First, the preferred nitrogen cluster under Ar f profiling, Si2N+, is extremely sensitive to small variations in the oxyge n content of the sample. The observed Si2N+ profile at the oxide/silicon in terface is largely influenced by these ionization yield changes. Second, ni trogen in oxynitrides is mobile under primary ion beam bombardment, an effe ct that is enhanced by the use of oxygen flooding, Under oxygen flooding, i t is demonstrated that nitrogen can diffuse through the oxide/silicon inter face far into the underlying silicon substrate. This investigation reveals that some of the reported nitrogen peak position s and tails should be interpreted as SIMS artefacts rather than as sample c haracteristics. Copyright (C) 2000 John Wiley & Sons, Ltd.